Variable resistance device



7 Feb. 20, 1934.

. A. O. CODNEY El AL VARIABLE RESISTANCE DEVICE Filed Dec. 24. 1931.1110 671607". ARTHUR 0. Canuev 1.2-4. 4- 0A WD J. SOMERVILLE PatentedFeb. 20, 1 934 UNITED STATES PATENT OFFICE VARIABLE RESISTANCE DEVICEApplication December 24, 1931 Serial No. 583,016

7 Claims.

This invention relates to variable resistance devices for use inelectric circuits, and more particularly to improved contact means forsuch devices.

An object of our invention is to provide a contact device of the typementioned, which is of improved and simplied construction, easilyoperated and very durable.

Another object of our invention is to provide a novel construction for arheostat contact of the type embodying a spring, wherein the arrangementis such that the spring operates at a relatively cool temperature andremains serviceable for a long period of time.

Other objects and advantages of our invention will be apparent from thefollowing description, when taken in conjunction with the accompanyingsheet of drawings, wherein Fig. 1 is a side elevational view of avariable resistance device embodying our invention.

Fig. 2 is a sectional plan view thereof, taken substantially on line2--2 of Fig. 1.

Fig. 3 is a sectional view taken on line 33 of Fig. 1.

Fig. 4 is a detail elevational view of the contact element, and

Fig. 5 is an end elevation thereof.

In the accompanying drawing to which detailed reference will now bemade, we have illustrated electrical resistance apparatus embodying thecontact means of our invention; and although we have shown but onestructural embodiment ofour device, it will be understood, of course,that our invention may assume various other forms.

As indicated in the drawing, our contact device, which may also bereferred to as a terminal device, is of the sliding type and is intendedfor use principally with rheostats of the wire wound type. Rheostats ofthis kind are commonly used for changing the resistance value of variouselectrical circuits, such as battery charging circuits and the like. Weare aware that sliding contacts have been used with rheostats of thiskind, but in the constructions heretofore proposed the contact deviceshave been short lived and generally unsatisfactory, principally byreason of the fact that the spring, which presses the contact elementagainst the resistance element, is positioned relatively close to thelatter element and is subjected to destructive heating thereby.

In Figs. 1 and 2 of the drawing we have shown a wire wound rheostat withwhich our contact device 11 cooperates. The rheostat may be of anysuitable construction, and as herein shown, may comprise a tubularinsulating body 12, having resistance wire 13 wound thereon. Anysuitable mount or frame may be provided for the rheostat, such as thespaced frame members 14.

For slidably supporting the contact device 11 in operative relation tothe resistance element, we provide a guide bar 15, which is preferablyround in cross-sectional shape, and which is formed of suitableconducting material. This guide is arranged with its axis substantiallyparallel to the axis of the insulating body 12, and may be supported inany appropriate manner, such as by being mounted in the frame memberswhich support the resistance element 13. Suitable means may be providedfor connecting the device in an electric circuit, such as the terminals16 and 17 mounted on one of the frame members 14. One end of theresistance wire of the rheostat is connected to'terminal 16 and theother terminal is connected to the guide bar 15, by a suitable conductor18, so that the rheostat may be connected in the desired relation in anelectric circuit by attaching conductors 19 and 20 to the terminals 16and 17.

The contact device itself comprises a tubular body 22 formed ofconducting material and having pivotal and sliding connectionintermediate its ends with the guide bar 15. This connection may beformed by providing aligned openings through the wall of the body inwhich opening the guide bar 15 slidably engages. As shown in thisinstance, we prefer to form these aligned openings as axially extendingslots 23. We mount the tubular body on the guide bar with the latterextending through the aligned openings and so that the body is disposedto extend substantially radially outwardly from the resistance element90 13, or, in other words, with its axis normal to the axis of the guidebar 15, as shown in Figs. 1 and 2. When disposed in this position, itwill be noted that the slotted end 24 of the tubular body extendsoutwardly from the guide bar in a direction away from the resistanceelement 13, while the unslotted end 25 of the tubular body extendsinwardly of the guide bar and towards the resistance element.

A contact element 26, formed of suitable COR-r ducting material, isprovided for engagement with the resistance element 13, and is arrangedfor movement relative to the tubular body. This contact element ispreferably formed with a stem 1 or plunger portion 27 which is slidablein the inner or unslotted end 25 of the tubular body, and a head or shoeportion 28 which engages the re sistance element 13. This shoe portionis of such shape and size as to afford the desired area of no contact,the particular shape of this portion being dependent upon the shape ofthe resistance element with which it cooperates. In this instance, theshoe portion is shown as having a concave contact face 29 ofsubstantially the same radius of curvature as the outer surface of theresistance element.

In accordance with our invention the stem portion of the contact elementis slotted for a portion of its length, as shown in Figs. 4 and 5, andis so proportioned that when slidably mounted in the end 25 of thetubular body, this slotted portion straddles the guide bar 15, and itsouter end 30 extends outwardly into the slotted end 24 of the tubularbody for a short distance, as indicated in Figs. 1 and 2. For pressingthe shoe portion of the contact element against the resistance element13, we arrange a coil spring 31 within the tubular body; As shown inFigs. 1 and 2 this coil spring is housed and guided in the outer orslotted end 24 of the tubular body, and cooperates with the stem portionof the contact element. One end of this spring engages a metallicbearing disc 32 provided at the forked end of the stem portion, and theother end of the spring engages abutment means provided on the body.This abutment means may be of any desired form, and may comprise abearing disc 33 retained in the opening of the tubular member by atransversely extending pin 34.

From the arrangement described it will be seen that when the device isassembled on the guide bar, the arcuate bottom portion of the slots 23of the tubular body provides bearing surfaces 35 which engage the outersurface of the guide bar 15. The coil spring interposed between the stemportion of the contact element and. the abutment means of the tubularbody, tends to cause relative sliding movement between these elements,whereby the bearing surfaces 35 are frictionally pressed against thesurface of the guide bar and the concave surface of the shoe portion 28is frictionally pressed against the outer surface of the resistanceelement 13. This biasing action of the spring results in proper electrical contact being made between the element 26 and the resistance element13, and also results in sufiicient friction being created between thetubular body and the guide bar, and between the contact element and theresistance element, to retain the contact device in any desired positionof adjustment along the axis of the rheostat. The concavity of the shoeportion of the contact element aifords an interengagement between thelatter and the resistance element, which, under the influence of thespring 31, tends to cause a self-centering of the contact element on theresistance element, and prevents the contact element from being easilyjarred out of engagement with the resistance element.

In our contact device, as herein illustrated and described, it will benoted that the coil spring 31 is positioned outwardly of the guide bar15 and is relatively remote from the resistance element 13, so that onlya small portion of the heat generated in the latter will be transmittedto the spring. Consequently the operating temperature of the spring canbe maintained at a relatively low value which will not destroy thetemper of the spring or impair its efficiency. It will also be notedthat the outwardly projected portion of the tubular body affords aprotective housing for the spring and also serves as a convenient handleportion by means of which the contact device may be slid along the guidebar.

Although in illustrating our invention we have shown the rheostat 10arranged with its axis in a vertical position, it should be understood,however, that the position of the rheostat is unimportant, and that ourcontact device will operate efficiently regardless of the particularmanner or position in which the rheostat may be supported. Likewise, itis immaterial to our invention whether the guide bar be supported on theframe of the rheostat, as shown in the drawing, or whether it beprovided with an independent support.

While we have illustrated and described the apparatus of our inventionin a detailed manner, it should be understood, however, that we do notintend to limit ourserves to the precise details of construction andarrangement of parts illustrated and described, but regard our inventionas including such changes and modifications as do not involve adeparture from the spirit of the invention and the scope of the appendedclaims.

Having thus described our invention what we claim is:

1. In a contact device for a resistance element, the combination of anelongated guide bar adjacent said element, a body mounted on said guidebar for sliding movement along the latter, said body being elongated andarranged to extend transversely of the guide bar with the ends of thebody extending in opposite directions from said guide bar, movablecontact means associated with one of the ends of said body including anactuating portion extending transversely of said guide bar, and a springassociated with the other end of said body and engaging said actuatingportion, said spring being effective for irictionally pressing said bodyagainst said guide and for yieldingly pressing said contact meansagainst said resistance element.

2. In apparatus of the character described the combination of aresistance element, a guide member adjacent thereto, a tubular bodyslidably mounted on said guide member with its axis extendingtransversely of the axis of the latter, a contact engaging said elementand having a stem slidable in one end of said body, said stem having aslotted portion extending transversely of said guide member, and aspring mounted in the other end of said body and engaging said stem.

3. The combination with a resistance element having a guide memberadjacent thereto, oi a contact device adapted to be moved along saidguide member and comprising an elongated body disposed with its axissubstantially normal to the axis of said guide member, said body beingprovided with an opening through which said guide member extends, acontact engaging said element and having a portion slidable relative tosaid body, said portion having a slot in registration with the openingof said body, abutment means on said body, and a spring interposedbetween said slidable portion and said abutment means, said spring beingefiective for frictionally pressing said body against said guide memberand for yieldingly pressing said contact against said resistanceelement.

4. The combination with a. resistance element having an elongated memberadjacent thereto, of a contact device slidable along said guide memberand comprising a tubular body extending transversely of the guide memberand having a slotted portion through which said guide member extends,said body being disposed with the slotted portion thereof extendingoutwardly from said guide member in a direction away from said element,a contact engaging said element and having a stem portion slidable insaid tubular body, and a spring disposed in the outwardly extendingportion of said body, said spring having portions cooperatingrespectively with said stem portion and with said outwardly extendingportion of the body whereby said contact is biased against said elementand said body is biased against said guide member.

5. The combination with a resistance element having an elongated guidemember adjacent thereto, of a terminal device slidable along said guidemember and comprising a body, a contact movable relative to said body,said body and contact being arranged to extend transversely of saidguide member with corresponding ends thereof extending outwardly fordifferent distances from said guide member and in a direction away fromsaid element, and resilient means cooperating with said ends and tendingto cause relative axial movement therebetween whereby said body is heldin engagement with said guide member and said contact is yieldinglypressed against said element.

6. The combination with a resistance element having a guide memberadjacent thereto, of a contact device adapted to be moved along saidguide member and comprising a body, a contact slidably mounted on saidbody, said contact and said body being provided with forked ends andarranged with said forked ends straddling said guide member andextending outwardly therefrom for different distances and in a directionaway from said element, and resilient means cooperating with said forkedends and tending to cause relative separating movement therebetweenwhereby said body is held in engagement with said guide member and saidcontact is yieldingly pressed against said element.

7. In a device of the character described the combination of aresistance element, an elongated support adjacent said element, a hollowbody having pivotal connection with said support, said pivotalconnection being such as to permit sliding movement of said body alongsaid support, a contact slidable in said hollow body between said pivotand said element, and a spring disposed in said hollow body for biasingsaid contact toward said element, said contact having means thereonshaped for cooperation with said element to normally prevent rotation ofsaid body relative to said support.

ARTHUR O. CODNEY. DAVID J. SOMERVILLE.

